The particle po shows distribution of quantities. It is traditionally classified as a preposition, but many use it as a particle with adverbial qualities.

Po has meaning only in relation to a number or quantity. Therefore, after po there must always be a number word or an expression of quantity: po kvin (by/at a rate of five), po dek (by/at a rate of ten), po dudek mil (by/at a rate of twenty thousand), po multe (by/at a rate of many), po kiom (by/at a rate of how many), po miliono (by/at a rate of a million), po duono (by/at a rate of half), po iom (by/at a rate of a few), po pluraj (by/at a rate of several), po paro (by/at a rate of a pair), po egalaj partoj (by/at a rate of equal parts), and so forth. Sometimes the quantity is understood through context: po pomo = po unu pomo (by/at a rate of [one/an] apple), po tutaj boteloj = po pluraj tutaj boteloj (by/at a rate of [several] whole bottles).

Po shows a portion of something, which is somehow distributed among several people, several things, several locations, or a similar situation. One portion belongs to each of the various things. To determine the whole quantity, the whole number, the po quantity should be multiplied by a number. This number depends on the context:

Por miaj kvar infanoj mi aĉetis dek du pomojn, kaj al ĉiu el la infanoj mi donis po tri pomoj. - For my four children I bought twelve apples, and to each one of the children I gave three apples.

3 apples times 4 = 12 apples. Note, that the result shows apples, not children. We multiplied 3 apples by the number of the children, but the result is definitely 12 apples, not 12 children. The result of this calculation always relates to whatever is indicated by the po expression.

Tie estis viro tre altkreska, kiu havis sur la manoj kaj sur la piedoj po ses fingroj, sume dudek kvar. - The very tall man who was there had, on his hands and on his feet, six fingers each, a total of twenty-four.

A hundred of those cigarettes cost 25 rubles. For five hundred of those cigarettes, the cost was therefore: 25 rubles times 5 = 125 rubles.

El ĉiuj vivaĵoj, el ĉiu karno, enkonduku po unu paro el ĉiuj en la arkeon, ke ili restu vivaj kun vi. - From all living things, from all flesh, lead one pair of each into the ark, that they stay alive with you.

If there were, for example, 1000 types of animals, there would be 2 animals (one pair) times 1000 = 2000 animals (1000 pairs).

Incorrect use of po

Po is often put before the wrong kind of expression. Here is a typical example:

Tiu ĉi ŝtofo kostas dek dolarojn po metro.
The speaker intends to say that ever ymetre of the cloth costs ten dollars, but that is incorrect. Here, po must relate to the word unu → po unu metro, understood through context. Therefore, the calculation becomes: 1 metre times 10 (the number of dollars) = 10 metres. In the sentence, po also appears before the expression (unu) metro ([one] metre). The result of the calculation is therefore ten metres, not ten dollars. Those ten metres of cloth cost one dollar. That was probably not the intended meaning.

If there is for example 5 meters, the calculation becomes: 10 dolors times 5 = 50 dollars. Now, the result shows dollars, because po (at the rate of) stands before the words dek dolaroj (ten dollars).

In these sorts of sentences, many languages use only one word to express distribution. This word is placed before metro (metre). Some people confuse po with these words, which have a completely different meaning than po. In Esperanto, these meanings are expressed with two words -- po (at a rate of) and one other. The other word is often por (for), but depending on the context, other prepositions (or an adverbial form) may be used. In the preceding example, the expressions laŭ metro or metre would also be possible.